The invention applies more particularly to the construction of a dynamoelectric rotating machine such as an alternator whose rotor has "superconducting" induction windings, i.e. windings made of a substance which becomes superconducting when it is cooled to a sufficiently low temperature e.g. 4.degree. K. (often referred to as "cryogenic"). Then, in addition to said electrical windings and the electric connection means necessary to supply current to them, the rotor further requires a cooling circuit to cool the windings from ambient temperature to said cryogenic temperature before operation of the alternator, and to keep the windings at said temperature during operation.
For each connection, said electric connection means include a cold current lead and a conventional rotating ring at ambient temperature. The ring co-operates with stationary brushes. The function of such a current lead is to ensure electric connection between an ordinary conductor at ambient temperature and one end of a superconductor while requiring as low a refrigerating power as possible to keep this end at cryogenic temperature despite the heat input from the current lead. The refrigerating power is the electrical or mechanical power needed by the refrigeration units such as helium liquefiers to keep the superconducting units at their normal operating temperature.
Such a current lead is described for example in U.S. Pat. No. 4,134,037.
The conductors are disposed longitudinally, i.e. parallel to the axis of the rotor, to ensure connection between the rings and the current leads. They are subject to severe conditions. Firstly, when the rotor is cooled (which is done at low rotation speed) the current leads shrink longitudinally to an appreciable extent. Secondly, the conductors connected to the collector rings expand during operation due to heating caused by the flow of a high electric current (between 5,000 and 10,000 amp) once the inductor is energized.
Further, it is necessary to take into account the danger of electric breakdown resulting from high voltages which can rise to 10 kV in the case of an incident. This danger is increased when the helium used is hot, since hot helium is a very poor dielectric.
Of course, connection can be ensured between the current leads and the rings by means of resilient corrugated conductors which can be formed for example by stacks of thin copper strips. However, such a solution is generally too bulky for the very small space that is available and in which screws cannot usually be used.
Preferred embodiments of the present invention provide a device for connecting a collector ring to a current lead of a superconducting rotor, which device allows reliable connection to be provided without giving rise to obstructive mechanical stress, without danger of electric breakdown or of faulty contact and without being too bulky.